| Motivated by the design of high energy lithium battery,anode materials with high capacity and suitable voltage are urgently needed to be explored to reach a higher energy density.In our work,the ladder-like?-Fe2O3 nanostructures,nanostructured porous Fe2N@C microcubes,homogeneous core–shell Ti-MnO2 NWs,liquid metal GaInSn as electrolyte deposited lithium metal,were designed and synthesized followed by systemtatic characterizations and electrochemical performance.The following results were achieved:?1?Thermal induced strain relaxation is realized to realizing the stable SEI control without the additional protective strategy.?-Fe2O3-800 have been fabricated through a template-engaged redox reaction followed by thermal treatment.The thermal treatment induces interfacial atomic rearrangement and results the formation of a series of 1D nanostructure.It is demonstrated that through thermal treatment,the lattice strain is largely relaxed and the defect density is well reduced,improving the interparticle contacts and contact at the interface of electrode,stabilizing the electrode/electrolyte interphase,facilitating the charge transfer.In this way,?-Fe2O3-800 is able to withstand the volume change upon charging/discharging without mechanical breaking and leads to a thin and stable SEI formation.As a result,the ladder-like?-Fe2O3 nanostructures obtained at 800 oC demonstrate an outstanding stable capacity of 1200 mA h g-1 at 100 mA g-1 and an excellent high-rate cyclability with a capacity fading of 0.056%per cycle for 1200 cycles at 5 A g-1.?2?A facile confined anion conversion method to obtain nanostructured porous Fe2N@C microcubes is developed.The Fe2N@C microcubes can resist the oxidation and keep Fe2N stable in the air.The well-designed Fe2N@C electrode displays very little volume expansion?9%?due to the readily formed confined space.Appropriate amount of internal voids in the Fe2N cubes is just enough to release the volume expansion during lithiation/delithiation processes.In this way,a high volumetric capacity of 1030 mAh cm-3?based on the lithiation electrode volume?is still achieved at a current density of 100 mA g-1,which is comparable to silicon anodes;at the same time,excellent high-rate cyclability is also obtained with a capacity retention of 91%after 2500 cycles even at 10 A g-1,which is rarely achieved among metal nitride electrodes.Kinetic analysis reveals that the Fe2N@C shows an enhanced contribution of capacitive charge mechanism and displays typical pseudocapacitive behavior,realizing the high rate performance for Fe2N@C microcube electrode.?3?Homogeneous core–shell Ti-MnO2 NWs.The Ti-MnO2 NWs with gradient Ti doping were composed of Ti-rich shells and Mn-rich cores.During the lithiation process,the Ti-rich shells showed smaller volume variations while the Mn-rich cores showed larger volume variations.In this way,gradient volume expansion from inner core to outer shell was achieved,which effectively released the stress of the NWs during the cycling and avoid the pulverization of the electrode.Moreover,the gradiently doped Ti is able avoid the Mn metal coarsening,reducing the metal particle size and improvig the reversibility of metal.In this way,the homogeneous core-shell Ti-MnO2 NWs enabled both high reversible areal and volumetrical capacity(2.3 mAh cm-22 and 991.3 mAh cm-3 at 200 mA g-1,respectively),reached a round-trip Coulombic efficiency of>99.5%after only 30 cycles,and retained an high capacity of 742 mAh g-1 after 3000 cycle at 10 A g-1 at a high mass loading level of 3mg cm-2.?4?The liquid metal GaInSn was used as additive in the electrolyte,and the effect of concentration of additives on the electrolyte was discussed.The electrochemcial performance of Li-Li symmetrical battery with liquid alloy GaInSn as electrolyte additive was studied for the first time.The voltage hysteresis after adding liquid alloy GaInSn as additive is still stable at 150 mV at high rate of 5 mA cm-2 during the rate performance test,while cell using the conventional electrolyte is unable to withstand the high current density,leading to very large voltage hysteresis.At the current density of 5 mA cm-2 and the areal specific capacity of 1 mAh cm-2,the polarization potential of Li-Li symmetrical cell with liquid alloy GaInSn was still lower than 400 mV after 1400 h of cycling.The organic composition of the solid electrolyte film formed on the surface of lithium metal by adding liquid alloy GaInSn as additive is the same as that of the commercial electrolyte without additive,but Ga is deposited as the additional inorganic component.Ga is deposited to the surface of lithium metal,and it is easy to form alloys with lithium metal.The common LiGa alloys are liquid metals at room temperature,so the growth of lithium dendrite can be inhibited.In this way,the coulombic efficiency of the battery was significantly improved by adding liquid alloy GaInSn as electrolyte additive when the specific area capacity could reach more than 2 mAh cm-2.The coulomb efficiency of the battery remained above 99%in the first 320 cycles and above 98%after 2500 cycles.After2500 cycles,the capacity of lithium metal batteries with liquid alloy GaInSn as electrolyte additive remained above 103 mAh g-1. |
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